I thought it would be Cpts., as in: "Captains Johansson and Riley were present" -> "Cpts. Johansson and Riley were present", but I cannot find anything definitive online.
Additionally, I would have just used Cpts., except I'm finding lots of results saying CPT should be capitalised, and/or should use Capt (or possibly Capt.) instead. So then I'm wondering if CPTs or CPTS would be the proper usage?
(This is in a purely military usage. And I suspect another issue is based on the country and branch being discussed. I have no specific branch intended. I am American but tend to use British English quite often.)